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Motorcycle Repair/ct 70 honda mini trail bike


Hello Mr S.  I have been working on an older 1981 Honda CT 70 mini trial bike that had set for about two years before i got it.  No History on this gem so I am curious if there is a way to check the primary coil on this bike.  I have removed it and checked for dead shorts and measure its resistance.  According to the CT manual i am ok as far as resistance goes on both stator coils as well as the external coil.  I just installed new points and condenser.  After the reinstall of my coils and points i now have no trigger voltage.  light coil measured at 1.2 ohms from white wire to ground terminal after windings and the second wire which was yellow measured only .7 ohms to ground lug.  No direct shorts so far.  The primary coil which is my spark coil measured 2.5 ohms to its ground lug.  I am at a loss due to my lack of magneto training.  Any help or direction i would greatly appreciate.  I had previously talked to Mr Silver.   Thanks in advance and you fellows are great.  Merry Christmas to you and your families and god bless.

Hi Joe,

The coils are usually pretty tough on these older Hondas.
The ignition coil behind the flywheel reads very low ohms
standard. Just make sure it is not open.

Ideally it would read about 1 ohm as the manual
states it might be internally shorted above that.

If you can't get any output it might need the lower coil.

Some other tips:

The points must be insulated from ground when open.
You may have to disconnect the condensor to check this.

If the points are not grounding except when closed
then they are okay. Flywheel should have some magnetism
on the inside with no rust.

Flywheel key must be good.

You can connect a multimeter to the black wire
and see if any voltage is coming from the lower coil
when you kickstart it.

You may just have
something shorting the output.
This might be in the points wire or connections.
Also the ignition switch or kill switch could
be an issue.

Look for anything that might ground the output

The system is fairly simple, the flywheel is magnetic
and induces a voltage in the lower coil.
When the points break open the voltage
can't go to ground so it rushes to the upper ignition coil
which then sparks the plug.

You can carefully check each component and hopefully
you will get some power. Sometimes new points
have an anticorrosive coating which must be buffed off
to get them to ground properly.

Points should not open too wide either as this
can cause them not to close and ground the coil.
Set it so the points just open on the "F" mark and it should work.


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Wayne S.


Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.


Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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